Communication devices such as User Equipments (UE) are also known as e.g. mobile terminals, wireless terminals and/or mobile stations. User equipments are enabled to communicate wirelessly in a wireless network, sometimes also referred to as a cellular radio system or cellular network. The communication may be performed e.g., between two user equipments, between a user equipment and a regular telephone and/or between a user equipment and a server. The communication may be performed e.g., via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the wireless network.
User equipments may further be referred to as mobile telephones, cellular telephones, or laptops with wireless capability, just to mention some further examples. The user equipments in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as user equipment or a server.
The wireless network covers a geographical area which is divided into cell areas, wherein each cell area is served by a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the user equipments within range of the base stations.
In some RANs, several base stations may be connected, e.g. by landlines or microwave, to a radio network controller, e.g. a Radio Network Controller (RNC) in Universal Mobile Telecommunications System (UMTS), and/or to each other. The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Spécial Mobile).
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
UMTS is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for user equipments. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
In network-controlled Device-to-Device (D2D) communications, a network such as a radio access network assists user equipments that are in the proximity of each other to discover one another, in a process referred to as device discovery, and establish a direct link referred to as D2D bearer establishment, rather than a link via the base station. In fact, when two user equipments communicate with each other via a cellular base station, the communication path involves an uplink and a downlink, both with associated resources, as opposed to the single hop direct D2D link.
Network-controlled D2D communication refers to two distinct cases in terms of the number of base stations or wireless access points, such as eNB, that are involved. In a single eNB case, both user equipments are connected or camp on, i.e. are served by the same eNB. In a multiple eNB case, the two devices that are candidates for direct D2D communications are served by different eNBs.
In network-controlled device discovery the radio access network may, for example, allocate resources for beacon signals, so that transmitting and receiving user equipments know what time and frequency resources being used for device discovery, that is when and at what frequencies beacons should be transmitted and scanned for or received. Alternatively, a user equipment may register at the network for D2D communications. Subsequently, another user equipment may inquire the network for possible peers allowing the network to mediate between, basically to match, the user equipments in finding each other.
The initiation of the establishment of the D2D link may be made by the radio access network or by any of the user equipments of the D2D pair. In network initiated D2D link establishment, the network realizes that two communicating user equipments are in the proximity of each other. In user equipment initiated D2D link establishment, the user equipments discover the proximity of each other and also some of their capabilities which is necessary for them to establish a D2D link, similar to Bluetooth.
In network-controlled D2D communication, a network control function performs at least one of: a) provisioning of a discovery signal to be used between two devices to determine their proximity and/or D2D link estimation, b) resource assignment for the D2D discovery signal and/or a D2D data channel and/or a D2D control channel, c) relaying of information between the at least two devices, and d) configuration of connection parameters for the at least two devices of the D2D link, such as power setting, e.g., actual, min, max, coding and modulation schemes, segmentation configuration, e.g., transport block sizes, parameters and/or security keys for encryption/integrity protection and protocol parameters.
The actual D2D transmission may then be either in the same spectrum as the network-device links or in separate spectrum, and may use another radio technology.
The actual D2D transmission does not need to be in licensed spectrum. In network controlled D2D only parts of the D2D link configuration, proximity detection need to be via licensed spectrum.
A D2D link may be initiated or maintained while the user equipments of the D2D pair are moving. However, if at least one of the user equipments of the D2D pair moves too quickly, two problems may arise: a) the D2D communication link may not be stable for a long time, which means that the D2D communication is likely to fail after short times; and/or b) the user equipments remain only temporarily connected to the network node controlling the communication, which means that the management and configuration of the D2D communication may likely fail after a short time.